Oh, Mom. Oh, Honey.

The five years I recently spent researching and writing a book about mothers and daughters also turned out to be the last years of my mother's life. In her late eighties and early nineties, she gradually weakened, and I spent more time with her, caring for her more intimately than I ever had before. This experience -- together with her death before I finished writing -- transformed my thinking about mother-daughter relationships and the book that ultimately emerged.

All along I had in mind the questions a journalist had asked during an interview about my research. "What is it about mothers and daughters?" she blurted out. "Why are our conversations so complicated, our relationships so fraught?" These questions became more urgent and more personal, as I asked myself: What had made my relationship with my mother so volatile? Why had I often ricocheted between extremes of love and anger? And what had made it possible for my love to swell and my anger to dissipate in the last years of her life?

Though much of what I discovered about mothers and daughters is also true of mothers and sons, fathers and daughters, and fathers and sons, there is a special intensity to the mother-daughter relationship because talk -- particularly talk about personal topics -- plays a larger and more complex role in girls' and women's social lives than in boys' and men's. For girls and women, talk is the glue that holds a relationship together -- and the explosive that can blow it apart. That's why you can think you're having a perfectly amiable chat, then suddenly find yourself wounded by the shrapnel from an exploded conversation.

Daughters often object to remarks that would seem harmless to outsiders, like this one described by a student of mine, Kathryn Ann Harrison:

"Are you going to quarter those tomatoes?" her mother asked as Kathryn was preparing a salad. Stiffening, Kathryn replied, "Well, I was. Is that wrong?"

"No, no," her mother replied. "It's just that personally, I would slice them." Kathryn said tersely, "Fine." But as she sliced the tomatoes, she thought, can't I do anything without my mother letting me know she thinks I should do it some other way?

I'm willing to wager that Kathryn's mother thought she had merely asked a question about a tomato. But Kathryn bristled because she heard the implication, "You don't know what you're doing. I know better."

I'm a linguist. I study how people talk to each other, and how the ways we talk affect our relationships. My books are filled with examples of conversa tions that I record or recall or that others record for me or report to me. For each example, I begin by explaining the perspective that I understand immediately because I share it: in mother-daughter talk, the daughter's, because I'm a daughter but not a mother. Then I figure out the logic of the other's perspective. Writing this book forced me to look at conversations from my mother's point of view.

I interviewed dozens of women of varied geographic, racial and cultural backgrounds, and I had informal conversations or e-mail exchanges with countless others. The complaint I heard most often from daughters was, "My mother is always criticizing me." The corresponding complaint from mothers was, "I can't open my mouth. She takes everything as criticism." Both are right, but each sees only her perspective.

One daughter said, for example, "My mother's eyesight is failing, but she can still spot a pimple from across the room." Her mother doesn't realize that her comments -- and her scrutiny -- make the pimple bigger.

Mothers subject their daughters to a level of scrutiny people usually reserve for themselves. A mother's gaze is like a magnifying glass held between the sun's rays and kindling. It concentrates the rays of imperfection on her daughter's yearning for approval. The result can be a conflagration -- whoosh .

This I knew: Because a mother's opinion matters so much, she has enormous power. Her smallest comment -- or no comment at all, just a look -- can fill a daughter with hurt and consequently anger. But this I learned: Mothers, who have spent decades watching out for their children, often persist in commenting because they can't get their adult children to do what is (they believe) obviously right. Where the daughter sees power, the mother feels powerless. Daughters and mothers, I found, both overestimate the other's power -- and underestimate their own.